Luminescent alphanumeric indicating tube having plural fluorescent layers

ABSTRACT

A luminescent alphanumeric indicating tube comprising an array of fluorescent segments formed on one surface of an insulating substrate, each segment including a carbon layer coated on the surface of the substrate and a first fluorescent layer interposed between the carbon layer and a second fluorescent layer, the first layer consisting fluorescent particles whose diameter is nearly equal to or smaller than that of the particles constituting the carbon layer and the second layer consisting of fluorescent particles whose diameter is larger than that of the particles consistuting the first fluorescent layer.

United States Patent Takeda et al. June 5, 1973 54] LUMINESCENT ALPHANUMERIC 3,249,559 5/1966 Gallas ..'..252 502 x INDI ATIN TUBE HAVING PLURAL 2,177,691 10 1939 Dawihl etal. ..313/109 FLUORESCENT LAYERS 2,829,295 4/1958 Gast et a1. ..313/109 Filed: Dec. 14, 1971 Appl. No.: 207,733

[73] Assignee:

[30] Foreign Application Priority Data Dec. 17, 1970 Dec. 30, 1970 Japan .45/1 12476 Japan .45/133895 US. Cl .313/108 R, 156/67, 313/1095 Int. Cl ..H0lj 1/66, HOlj l/68 Field of Search ..313/108 R, 108 A, 313/1095, 109; 156/67; 117/335 C;

[56] References Cited UNITED STATES PATENTS 3,508,101 4/1970 Tanji ..3l3/1095 Primary ExaminerPalmer C. Demeo Attorney-Robert D. Flynn, Stephen H. Frishauf, Leonard l-loltz et al.

[57] ABSTRACT A luminescent alphanumeric indicating tube comprising an array of fluorescent segments formed on one surface of an insulating substrate, each segment including a carbon layer coated on the surface of the substrate and a first fluorescent layer interposed between the carbon layer and a second fluorescent layer, the first layer consisting fluorescent particles whose diameter is nearly equal to or smaller than that of the particles constituting the carbon layer and the second layer consisting of fluorescent particles whose diameter is larger than that of the particles consistuting the first fluorescent layer.

3 Claims, 4 Drawing Figures LUMINESCENT ALPI-IANUMERIC INDICATING TUBE HAVING PLURAL FLUORESCENT LAYERS This invention relates to a luminescent indicating tube, and more particularly to a luminescent alphanumeric indicating tube comprising means for emitting electrons or ion particles and fluorescent means including an insulating substrate and an array of fluorescent segments formed on one surface of the substrate, each segment being insulated from the other and selectively activated by impingement of emitted electrons or ion particles to present a desired pattern of luminescence.

The above-mentioned type of fluorescent alphanumeric indicating tube has already been disclosed in the U.S. Pat. No. 3,508,101 and an American engineering journal Electronics, May 29, 1967, pp. 212 to 213, and is generally used with relatively low voltage (say, about 20 volts). The conventional fluorescent segment of such fluorescent alphanumeric indicating tube is usually formed in the manner described as below. First, there is deposited a conductive layer on one surface of the insulating substrate in a suitable known manner. Then this substrate is placed in the bottom of a vessel filled with a suspension which suspending fluorescent particles and metal ions of potassium or lithium as a binder, and the fluorescent particles and metal ions are sedimented on the surface of the substrate to form a fluorescent layer on the conductive layer. Said metal ions included in the sedimentary fluorescent layer thus prepared undesirably reduce the luminescence of the fluorescent layer, where it is impinged by electrons or ions of low energy. The prior art indicating tube, therefore, contains as small amounts as possible of ions of metals acting as a binder of fluorescent materials, and consequently has the drawback that due to the reduced content of such binder, the fluorescent segment of the conventional indicating tube is bonded to the conductive layer with extremely low strength.

It is accordingly the object of this invention to provide a fluorescent alphanumeric indicating tube wherein the fluorescent layer is firmly bonded to the conductive layer and moreover provided with a fluorescent segment capable of becoming luminescent with fully great brightness even when impinged by electrons or ions of relatively low energy.

SUMMARY OF THE INVENTION According to this invention, there is provided a luminescent indicating tube comprising means for emitting electrons or ion particles and fluorescent means including an insulating substrate and an array of fluorescent segments disposed on one surface of said substrate, each segment being insulated from the other and selectively activated by impingement of emitted electrons or ion particles so as to present a desired pattern of luminescence characterized in that each fluorescent segment comprises a carbon layer deposited on the surface of the substrate; a first fluorescent layer superposed on said carbon layer and formed of particles of fluorescent materials, most of which have a substantially smaller diameter than the particles constituting said carbon layer; and a second fluorescent layer mounted on said first fluorescent layer and consisting of particles of fluorescent materials, most of which have a substantially larger diameter than the particles constituting said first fluorescent layer.

The present invention can be more fully understood from the following detailed description when taken in conjunction with the appended drawings, in which:

FIG. 1 is a sectional view of a fluorescent'indicating tube according to this invention;

FIG. 2 is a perspective view of the luminescent anode of the fluorescent indicating tube of FIG. 1;

FIG. 3 is a cross sectional view on line AA of the luminescent anode of FIG. 2 as taken in the direction of the indicated arrows; and

FIG. 4 schematically illustrates the method of manufacturing the luminescent segments of FIG. 2.

Referring to FIG. 1, numeral 1 represents a fluorescent alphanumeric indicating tube which comprises a vacuum envelope 2 made of transparent glass, thermal electron emitting filament 3, netlike acceleration electrode 4, mask 5 for distinctly indicating patterns, for example, letters and luminescent anode 6, all these elements being sealed hermetically within said envelope. The electrode elements are connected to outer leads 8 comprised of conductive rods by inner leads 7 formed of conductive wires.

The luminescent anode or electrode 6 comprises, as shown in FIGS. 2 and 3, an insulating substrate 10 made of, for example, ceramic material and a plurality of fluorescent segments 14 arranged on the surface of said substrate in a suitable mosaic pattern. Each fluorescent segment 14 comprises a conductive layer 12 formed of graphite or carbon, a first fluorescent layer 15 consisting of fluorescent particles whose diameter is nearly equal to or smaller than that of the particles constituting said conductive layer 12 and a second fluorescent layer 16 consisting of fluorescent particles whose diameter is larger than that of the particles constituting said first fluorescent layer 15. Said fluorescent segments are deposited on the grooves 11 formed on one surface of the insulating substrate 10. The conductive layer 12 contacts the inner leads 7 penetrating the insulating substrate 10.

The indicating tube 1 arranged as described above is put into operation when the outer leads 8 are impressed with prescribed voltage. At this time there are emitted thermal electrons from the filament 3. Said thermal electrons are directed to the fluorescent anode 6 by the acceleration anode 4. When the desired fluorescent segments 14 are selectively impressed with positive voltage through the outer leads 8, then said segments are impinged by electrons to project luminescent, presenting a luminous pattern, for example, desired numerals.

The fluorescent segment of this invention is prepared in the following manner. Powders of carbon or graphite consisting of extremely fine particles whose average diameter ranges from about 3 to 5 microns are mixed with an aqueous suspension suspending a vitreous binder material mainly composed of potassium oxide. Said mixture is applied, for example, by the known spray method to that side of the insulating substrate of ceramic material in which there is formed the aforesaid groove 11. After being coated with said mixture, the substrate 10 is baked in the air heated to a temperature of 400 to 500 C. Unnecessary carbon deposited on the other parts of the surface of the substrate 10 than the bottom of the groove 11 is eliminated by proper means, obtaining the required conductive carbon layer 12 at the groove bottom.

On this carbon layer is superposed a first fluorescent layer through the following steps. First, one of the known fluorescent materials (zinc oxide according to this embodiment) is taken into deionized water. The zinc oxide in the deionized water is stirred and milled together with glass beads about 1 to 5 millimeters in diameter which are added to this water, and there is obtained a suspension of zinc oxide particles. The particle size distribution of this zinc oxide suspension falls within a certain range. In this embodiment, the fluorescent zinc oxide has an average particle size of about 4 microns. From the suspension are selected finer particles by water screening in the following manner. The suspension is poured into a vessel and left intact several minutes in a place less subject to vibration. As is well ,known, larger particles settle quicker than smaller ones. Then, this suspension is skimmed, there are separated a suspension containing finer particles. The size of particles of this suspension thus separated can be easily controlled by the length of time for which the formersuspension is left intact. In the case of this embodiment, the water-screened fluorescent particles mostly had a size of less than 2 microns.

The suspension obtained by the aforesaid processes which contains the finer fluorescent particles 24 is taken from a beaker 23 into the deionized water 22 filled in a vessel 21, as shown in FIG. 4. At the bottom of the vessel 21, there is placed the ceramic substrate having the conductive carbon layer 12 formed at the bottom of the groove 11. The fluorescent particles 24 gravitationally settle down on the ceramic substrate 10 to form a fluorescent layer on the surface of said substrate 10 as well as on the conductive carbon layer 12. According to this embodiment, said first fluorescent layer 15 is about 10 microns thick.

On the first fluorescent layer 15 is deposited a second fluorescent layer 16 in the same manner as in the formation of the first layer. Now, there are prepared a suspension containing layer fluorescent particles by the water screening process. These larger particles suspended in the deionized water are deposited on the first fluorescent layer 15 by sedimentation to form the second fluorescent layer 16. According to this embodiment, this second fluorescent layer 16 is about 40 microns thick and consists of particles, most of which have a size of more than 2 microns. The deionized water 22 is removed. Then the substrate 10 is thermally dried. After drying unnecessary fluorescent material attached to the other parts of the substrate surface than that on which there is formed the conductive carbon layer 12 is brushed off, thus obtaining a first fluorescent layer 15 on said conductive carbon layer 12. Since the second fluorescent layer 16 is formed in the same way as the first fluorescent layer 15, description thereof is omitted.

The fluorescent segment 14 thus prepared can be bonded to the substrate 10 very firmly. The reason is supposed to be that in the interface between the conductive carbon layer and the first fluorescent layer 15, the relatively finer particles of the fluorescent material are intermeshed with the relatively larger carbon particles. Moreover, said fluorescent segment 14 displays extremely high luminescence. This is because the second fluorescent layer 16 consisting of relatively large particles constitutes the top surface of said segment 14 and also because the first and second fluorescent layers are free from metal ions which give rise to low luminescence.

The foregoing description refers to the case where there was used the indicating of display tube which indicates any one of a group of characters or numerals. However, this invention is also applicable to an indicating tube of the type which indicates a plurality of numerals or characters simultaneously, such as a number comprising a plurality of digits. Such type of fluorescent indicating tube includes a hermetically sealed vac uum envelope and a filament disposed within said envelope. An alignment of a plurality of fluorescent anodes is placed within said single envelope, each anode comprising an insulating substrate and an array of fluorescent segments is prepared in the aforementioned manner. Further, the above-mentioned embodiment refers to a vacuum fluorescent display tube utilizing electrons. Where, however, this invention is applied to a discharge fluorescent display tube which comprises a glass envelope sealed with ionizable gases, for example, neon, an anode and fluorescent cathode segments arranged within said envelope and carries out display by projecting luminescence from said fluorescent cathode by impingement of ions occuring in discharge, it is advised to use as a cathode a luminescent electrode 6 comprising an insulating substrate on which there are formed the aforesaid fluorescent segments 14.

What we claim is:

l. A luminescent alphanumeric indicating tube comprising a sealed transparent envelope containing means for emitting electrons and fluorescent means including an insulating substrate and an array of fluorescent segments disposed on one surface of said substrate, each of said fluorescent segments being insulated from the other and being selectively activated by impingement of emitted electrons so as to present a desired pattern of luminescence, each fluorescent segement comprisa carbon layer comprised of carbon particles deposited on the surface of the substrate;

a first fluorescent layer superposed on said carbon layer and substantially consisting of particles of fluorescent material which have a diameter which is smaller than the diameter of the particles constituting said carbon layer; and

a second fluorescent layer superposed on said first fluorescent layer and substantially consisting of particles of fluorescent material which have a substantially larger diameter than the diameter of the particles constituting said first fluorescent layer.

2. A luminescent alphanumeric indicating tube according to claim 1 wherein said first and second layers of fluorescent materials substantially do not include any metal ion.

3. A luminescent alphanumeric indicating tube according to claim 1 wherein said first fluorescent layer is substantially composed of particles of fluorescent materials having a smaller diameter than two microns,

' and said second fluorescent layer is substantially comprised of particles of fluorescent materials having a larger diameter than two microns.

UNITED STATES PATENT OFFICE CER'EE FECATE ()F CORECTEON Patent No. 3 737 705 Dated June 5, 1973 In Mitsuo TAKEDA et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract:

line 7, after "consisting insert -of;

Column 4, line 59 change "composed" to '-comprised.

Signed and sealed this 27th day of November 1973 (SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents RM PO-1050 (10-69) I USCOMM-DC 60376-P69 fr u.s. GOVERNMENT PRINTING OFFIVCE: 1969 0-365-334. 

2. A luminescent alphanumeric indicating tube according to claim 1 wherein said first and second layers of fluorescent materials substantially do not include any metal ion.
 3. A luminescent alphanumeric indicating tube according to claim 1 wherein said first fluorescent layer is substantially composed of particles of fluorescent materials having a smaller diameter than two microns, and said second fluorescent layer is substantially comprised of particles of fluorescent materials having a larger diameter than two microns. 